[FFmpeg-devel] [PATCH v4 22/22] avdevice/dshow: capabilities query also works on opened device

[Diederick Niehorster <dcnieho@gmail.com>]

While the capabilities API is in principle meant to be used with an
allocated format context belonging to an unopened device, small changes
make it work for an opened dshow device as well. So hereby done.

Signed-off-by: Diederick Niehorster <dcnieho@gmail.com>
---
 libavdevice/dshow.c         | 110 +++++++++++++++++++++---------------
 libavdevice/dshow_capture.h |   3 +
 2 files changed, 66 insertions(+), 47 deletions(-)

diff --git a/libavdevice/dshow.c b/libavdevice/dshow.c
index c426cef905..216c888bed 100644
--- a/libavdevice/dshow.c
+++ b/libavdevice/dshow.c
@@ -849,7 +849,7 @@ dshow_cycle_formats(AVFormatContext *avctx, enum dshowDeviceType devtype,
     void *caps = NULL;
     int i, n, size, r;
     int wait_for_better = 0;
-    int use_default;
+    int use_default, already_opened;
 
     // format parameters requested by user
     // if none are requested by user, the values will below be set to
@@ -875,6 +875,9 @@ dshow_cycle_formats(AVFormatContext *avctx, enum dshowDeviceType devtype,
     if (!caps)
         goto end;
 
+    // get if device is already opened
+    already_opened = ctx->device_name[0] || ctx->device_name[1];
+
     /**
      * If we should open the device with the default format,
      * then:
@@ -1153,7 +1156,7 @@ dshow_cycle_formats(AVFormatContext *avctx, enum dshowDeviceType devtype,
         // in ranges, try to apply in all cases, and store
         // caps if successfully applied
         if (!wait_for_better || ranges) {
-            if (IAMStreamConfig_SetFormat(config, type) != S_OK)
+            if (!already_opened && IAMStreamConfig_SetFormat(config, type) != S_OK) // skip if device already opened
                 goto next;
             else if (ranges) {
                 // format matched and could be set successfully.
@@ -1494,12 +1497,19 @@ dshow_list_device_options(AVFormatContext *avctx, ICreateDevEnum *devenum,
     char *device_unique_name = NULL;
     int r;
 
-    if ((r = dshow_cycle_devices(avctx, devenum, devtype, sourcetype, &device_filter, &device_unique_name, NULL)) < 0)
-        return r;
-    ctx->device_filter[devtype] = device_filter;
-    ctx->device_unique_name[devtype] = device_unique_name;
+    if (!ctx->device_filter[devtype]) {
+        if ((r = dshow_cycle_devices(avctx, devenum, devtype, sourcetype, &device_filter, &device_unique_name, NULL)) < 0)
+            return r;
+
+        // put them in context so they'll be cleaned up again
+        ctx->device_filter[devtype] = device_filter;
+        ctx->device_unique_name[devtype] = device_unique_name;
+    } else
+        device_filter = ctx->device_filter[devtype];
+
     if ((r = dshow_cycle_pins(avctx, devtype, sourcetype, device_filter, ranges ? &device_pin : NULL, ranges, query_type)) < 0)
         return r;
+
     return 0;
 }
 
@@ -2319,7 +2329,8 @@ fail1:
     return ret;
 }
 
-// fake class to point av_opt_query_ranges to our query_ranges function
+// fake class to point av_opt functions to capabilities that can be queried,
+// and av_opt_query_ranges to our query_ranges function
 static const AVClass dshow_dev_caps_class = {
     .class_name   = "",
     .item_name    = av_default_item_name,
@@ -2337,49 +2348,51 @@ static int dshow_create_device_capabilities(struct AVFormatContext *avctx, AVDev
     // set class so queries work
     caps->av_class = &dshow_dev_caps_class;
 
-    if (ctx->device_name[0] || ctx->device_name[1]) {
-        av_log(avctx, AV_LOG_ERROR, "You cannot query device capabilities on an opened device\n");
-        ret = AVERROR(EIO);
-        goto fail;
-    }
+    // check if device setup is needed or we will be querying capabilities of an already opened device
+    ctx->cap_query_already_opened = ctx->device_name[0] || ctx->device_name[1];
+    if (ctx->cap_query_already_opened)
+        av_log(avctx, AV_LOG_WARNING, "Querying device capabilities on an opened device: may yield false positives\n");
 
-    if (!parse_device_name(avctx)) {
-        av_log(avctx, AV_LOG_ERROR, "You must set a device name (AVFormatContext url) to specify which device to query capabilities from\n");
-        ret = AVERROR(EINVAL);
-        goto fail;
-    }
-
-    CoInitialize(0);
-    if (CoCreateInstance(&CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER,
-                         &IID_ICreateDevEnum, (void **) &devenum)) {
-        av_log(avctx, AV_LOG_ERROR, "Could not enumerate system devices.\n");
-        ret = AVERROR(EIO);
-        goto fail;
-    }
+    // if device not already opened, check that what user specified can be opened
+    if (!ctx->cap_query_already_opened) {
+        if (!parse_device_name(avctx)) {
+            av_log(avctx, AV_LOG_ERROR, "You must set a device name (AVFormatContext url) to specify which device to query capabilities from\n");
+            ret = AVERROR(EINVAL);
+            goto fail;
+        }
 
-    // check devices can be found
-    if (ctx->device_name[VideoDevice]) {
-        IBaseFilter *device_filter = NULL;
-        char *device_unique_name = NULL;
-        if ((ret = dshow_cycle_devices(avctx, devenum, VideoDevice, VideoSourceDevice, &device_filter, &device_unique_name, NULL)) < 0)
-            return ret;
-
-        if (ret >= 0) {
-            ctx->device_filter[VideoDevice] = device_filter;
-            ctx->device_unique_name[VideoDevice] = device_unique_name;
+        CoInitialize(0);
+        if (CoCreateInstance(&CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER,
+                             &IID_ICreateDevEnum, (void **) &devenum)) {
+            av_log(avctx, AV_LOG_ERROR, "Could not enumerate system devices.\n");
+            ret = AVERROR(EIO);
+            goto fail;
         }
-    }
-    if (ctx->device_name[AudioDevice]) {
-        IBaseFilter *device_filter = NULL;
-        char *device_unique_name = NULL;
-        if (dshow_cycle_devices(avctx, devenum, AudioDevice, AudioSourceDevice, &device_filter, &device_unique_name, NULL) < 0) {
-            /* try to access audio from combined video+audio sources as fallback */
-            if ((ret = dshow_cycle_devices(avctx, devenum, AudioDevice, VideoSourceDevice, &device_filter, &device_unique_name, NULL)) < 0)
-                goto fail;
+
+        // check devices can be found
+        if (ctx->device_name[VideoDevice]) {
+            IBaseFilter *device_filter = NULL;
+            char *device_unique_name = NULL;
+            if ((ret = dshow_cycle_devices(avctx, devenum, VideoDevice, VideoSourceDevice, &device_filter, &device_unique_name, NULL)) < 0)
+                return ret;
+
+            if (ret >= 0) {
+                ctx->device_filter[VideoDevice] = device_filter;
+                ctx->device_unique_name[VideoDevice] = device_unique_name;
+            }
         }
-        if (ret >= 0) {
-            ctx->device_filter[AudioDevice] = device_filter;
-            ctx->device_unique_name[AudioDevice] = device_unique_name;
+        if (ctx->device_name[AudioDevice]) {
+            IBaseFilter *device_filter = NULL;
+            char *device_unique_name = NULL;
+            if (dshow_cycle_devices(avctx, devenum, AudioDevice, AudioSourceDevice, &device_filter, &device_unique_name, NULL) < 0) {
+                /* try to access audio from combined video+audio sources as fallback */
+                if ((ret = dshow_cycle_devices(avctx, devenum, AudioDevice, VideoSourceDevice, &device_filter, &device_unique_name, NULL)) < 0)
+                    goto fail;
+            }
+            if (ret >= 0) {
+                ctx->device_filter[AudioDevice] = device_filter;
+                ctx->device_unique_name[AudioDevice] = device_unique_name;
+            }
         }
     }
 
@@ -2395,9 +2408,12 @@ fail:
 
 static int dshow_free_device_capabilities(struct AVFormatContext *avctx, AVDeviceCapabilitiesQuery *caps)
 {
+    struct dshow_ctx *ctx = avctx->priv_data;
+
     // clear state variables that may have been set during the querying process
     // (e.g. frees device names, removes device_filters, etc)
-    dshow_read_close(avctx);
+    if (!ctx->cap_query_already_opened)
+        dshow_read_close(avctx);
 
     return 0;
 }
diff --git a/libavdevice/dshow_capture.h b/libavdevice/dshow_capture.h
index 94ba9896b7..a2c107b19c 100644
--- a/libavdevice/dshow_capture.h
+++ b/libavdevice/dshow_capture.h
@@ -345,6 +345,9 @@ struct dshow_ctx {
     int sample_rate;
     int sample_size;
     int channels;
+
+    // for capabilities query
+    int cap_query_already_opened;
 };
 
 /*****************************************************************************
-- 
2.28.0.windows.1

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